This invention relates to a circuit-connecting material to be interposed between circuit electrodes acing each other and, the facing electrodes being pressed against each other, to electrically connect the electrodes in the pressing direction. It also relates to a circuit terminal connected structure and a circuit terminal connecting method.
Epoxy resin adhesives are widely used for various purposes of electric, electronic, construction, automobile, aircraft and so forth because they can attain a high bonding strength and have excellent water resistance and heat resistance. In particular, one-part epoxy resin adhesives are used in the form of films, pastes or powders because they make it unnecessary to mix the base resin and the curing agent and can be used with ease. In this case, it is general to attain specific performances by using epoxy resins, curing agents and modifiers in various combinations (e.g., Japanese Patent Application Laid-open (KOKAI) No. 62-141083).
However, film type epoxy resin adhesives as disclosed in the above Japanese-Patent Application Laid-open (KOKAI) No. 62-141083, though having an excellent operability, have been required to be heated at about 140 to 180xc2x0 C. when connected in a time of about 20 seconds, and at about 180 to 210xc2x0 C. when connected in 10 seconds.
This is because catalyst type curing agents, which are inert at normal temperature, are used so that both short-time curability (rapid curability) and storage stability (storability) can be achieved to attain a better stability, and hence no sufficient reaction can take place when cured.
In recent years, in the field of precision electronic equipment, circuits are being made higher in density, resulting in very small width of electrodes and very narrow spaces between electrodes. Hence, there has been a problem that the wiring comes off, separates or positionally deviates under connecting conditions for circuit-connecting materials making use of conventional epoxy resin adhesives. Also, in order to improve production efficiency, it is increasingly sought to shorten the connecting time to 10 seconds or less, making it indispensable to attain low-temperature rapid curability.
The present invention provides an electric and electronic circuit-connecting material having a superior low-temperature rapid curability and also having a long pot life.
A first circuit-connecting material of the present invention is a circuit-connecting material which is interposed between circuit electrodes facing each other and electrically connects the electrodes in a the pressing direction by pressing the facing electrodes against each other;
the circuit-connecting material comprising as essential components the following components (1) to (3):
(1) a curing agent capable of generating free radicals upon heating;
(2) a hydroxyl-group-contalning resin having a molecular weight of 10,000 or more; and (3) a radical-polymerizable substance.
As the curing agent capable of generating free radicals upon heating, preferred are curing agents having a 10-hour half-life temperature of 40xc2x0 C. or above and a 1-minute half-life temperature of 180xc2x0 C. or below, and peroxyesters are usable.
The radical-polymerizable substance may contain radical-polymerizable substance represented by the following chemical formula (a). 
wherein n is an integer of 1 to 3.
As the hydroxyl-group-containing resin having a molecular weight of 10,000 or more, preferred are phenoxy resins, in particular, phenoxy resins modified with a carboxyl-group-containing elastomer and phenoxy resins modified with an epoxy-group-containing elastomer.
A second circuit-connecting material of the present invention is a circuit-connecting material which is interposed between circuit electrodes facing each other and electrically connects the electrodes in the pressing direction by pressing the facing electrodes against each other;
the circuit-connecting material comprising as essential components the following components (3)and (4):
(3) a curing agent capable of generating free radicals upon heating and having a 10-hour half-life temperature of 40xc2x0 C. or above and a 1-minute half-life temperature of 180xc2x0 C. or below; and
(4) a radical-polymerizable substance.
As the curing agent capable of generating free radicals upon heating, peroxyesters are preferred.
The circuit-connecting material described above may contain an acrylic rubber.
A third circuit-connecting material of the present invention is a circuit-connecting material which is interposed between circuit electrodes facing each other and electrically connects the electrodes in the pressing direction by pressing the facing electrodes against each other;
the circuit-connecting material having, in the measurement with a differential scanning calorimeter (DSC) at 10xc2x0 C./min., an exothermic reaction arising temperature (Ta) within a range of from 70xc2x0 C. to 110xc2x0 C., a peak temperature (Tp) of Ta+5 to 30xc2x0 C. and an end temperature (Te): of 160xc2x0 C. or below.
The above circuit-connecting material may contain conductive particles.
The circuit terminal connected structure of the present invention comprises a first circuit member having a first connecting terminal and a second circuit member having a second connecting terminal;
the circuit members being disposed in such a way that the first connecting terminal and the second connecting terminal face each other; the circuit-connecting material described above being interposed between the first connecting terminal and the second connecting terminal which face each other;
and the first connecting terminal and the second connecting terminal which face each other being electrically connected.
The circuit terminal connecting method of the present invention comprises;
disposing a first circuit member having a first connecting terminal and a second circuit member having a second connecting terminal, in such a way that the first connecting terminal and the second connecting terminal face each other and interposing the circuit-connecting material described above, between the first connecting terminal and the second connecting terminal which face each other, followed by heating and pressing to electrically connect the first connecting terminal and the second connecting terminal which face each other.
The circuit terminal connected structure of the present invention may also comprise a first circuit member having a first connecting terminal and a second circuit member having a second connecting terminal;
the circuit members being disposed in such a way that the first connecting terminal and the second connecting terminal face each other; a circuit-connecting material capable of curing upon radical polymerization being interposed between the first connecting terminal and the second connecting terminal which face each other; the surface of at least one of the first and second connecting terminals being formed of a metal selected from gold, silver, tin and platinum group metals; and the first connecting terminal and the second connecting terminal which face each other being electrically connected.
The circuit terminal connecting method of the present invention may also comprise;
disposing a first circuit member having a first connecting terminal and a second circuit member having a second connecting terminal, in such a way that the first connecting terminal and the second connecting terminal face each other and interposing a circuit-connecting material capable of curing upon radical polymerization, between the first connecting terminal and the second connecting terminal which face each other, followed by heating and pressing to electrically connect the first connecting terminal and the second connecting terminal which face each other;
the surface of at least one of the first and second connecting terminals being formed of a metal selected from gold, silver, tin and platinum group metals; and the circuit-connecting material capable of curing upon radical polymerization being formed on one connecting terminal whose surface is formed of the s metal selected from gold, silver, tin and platinum group metals, and thereafter the other connecting terminal being registered, followed by the heating and pressing to connect them.